The invention relates to a luminaire provided with a lamp housing and holders for accommodating several electric lamps of different color aspect next to one another in the lamp housing, said housing having a non-transparent, light-transmitting window for allowing light to issue to the exterior.
Such a luminaire is known from JP-A-0 800 7611. In the known luminaire, three fluorescent lamps are accommodated next to one another inside the lamp housing, each surrounded by a filter in the respective colors red, green, and blue. The luminous flux of each lamp can be independently controlled, so that the color of the emerging light can be adjusted. The window is arranged opposite the lamps and is of a xe2x80x9cmilkyxe2x80x9d consistency. Requirements are imposed on the minimum distance of the lamps to the window and on the width of the window in relation to its distance to the lamps for the purpose of mixing the light coming from the lamps before it issues through the window.
It is a disadvantage of the known luminaire that the lamp housing is comparatively voluminous for the purpose of mixing the generated light. Another disadvantage is that there is a risk of inhomogeneity of the color of the window, so that color differences are visible. A major disadvantage is also that the efficiency of the luminaire is comparatively low.
It is an object of the invention to provide a luminaire of the kind described in the opening paragraph which is suitable for illuminating spaces with light of a chosen color aspect, which is efficient, and which has a construction allowing a compact shape.
According to the invention, this object is achieved in that a reflector with a reflection coefficient of at least 0.85 is present in the lamp housing, which reflector is positioned so as to surround at least substantially lamps arranged in the holders and which leaves the window free, in that the window has a surface area accounting for 10 to 70% of the total surface area of the reflector and the window together, and in that the window affords access to a reflector housing which comprises means for shaping light issuing through the window into a beam.
The means for shaping the light issuing through the window into a beam prevent a radiation in all directions and ensure that the light will arrive mainly there where it is desired, for example on a workbench or on a wall. The means may also serve to avoid that the light arrives where it is not desired, for example on a picture screen where it would cause unpleasant reflections. The luminaire thus has a property which is required for its application in space illumination. The means contribute to the efficiency of the luminaire.
Reflection of light on the reflector causes the light of the lamps accommodated in the holders to be mixed, while loss of light is effectively counteracted thereby. It is important in this respect that the reflection coefficient is comparatively high and is at least 0.85. This also contributes to the efficiency of the luminaire. The relative surface area of the window is also important for a good mixing, because a comparatively large window, larger than 70%, will give an insufficient mixing through reflections and because a comparatively small window, smaller than 10%, will cause losses owing to absorption by the reflector which are generally comparatively great. The good mixing of the light of the lamps owing to the reflections in the lamp housing means that the lamp housing can be compact. The window is illuminated with an at least substantially homogeneous color and acts as a secondary light source whose light is concentrated into a beam in the reflector housing and is thus further mixed. The possibility of having a compact lamp housing renders possible a comparatively small window, and thus a compact reflector housing and a compact luminaire.
It is favorable for counteracting light losses if the reflector in the lamp housing has a reflection coefficient of at least 0.90. Furthermore, it is preferred that the window has a surface area amounting to 50 to 60% of the total surface area of the reflector and the window, because a very good mixing of light is obtained in that case, while light losses are minimized.
The luminaire may be used for lighting spaces, in which case the color aspect of the light can be adapted to the circumstances, for example to the incoming daylight, the personal taste of the user, or the nature of the work carried out in the spaces.
It is favorable when the holders of the luminaire are suitable for accommodating fluorescent lamps, in particular elongate tubular fluorescent lamps. Fluorescent lamps have a comparatively high luminous efficacy and may themselves have a chosen color aspect. The term xe2x80x9ccolor aspectxe2x80x9d here denotes both the xe2x80x9ccolorxe2x80x9d itself, such as a color of the rainbow such as a primary color red, green, or blue, as well as the xe2x80x9ccolor temperaturexe2x80x9d such as, for example, 2700 K and 6500 K. The color temperature of a lamp here indicates the temperature of a black body whose radiation substantially corresponds to thexe2x80x94whitexe2x80x94light of the lamp.
Fluorescent lamps radiate light having a color or a color temperature in that ultraviolet radiation generated in the electric discharge inside the lamps is directly converted into light by a fluorescent material or a mixture of fluorescent materials in the lamps. The lamps themselves have a high luminous efficacy, i.e. without the use of filters which absorb light which is accordingly lost, given the efficient fluorescent substances usual nowadays.
Tubular fluorescent lamps have one or two contact pins at both ends of their tubes, by means of which they can be accommodated in suitable holders arranged for contacting of a pin, for holding them mechanically, and for supplying them electrically. The holders for these lamps cooperate in pairs for holding a lamp. Tubular fluorescent lamps having two substantially parallel tube portions in series have their contact pins next to one another at free ends of the tube portions. These lamps have the advantage that they are supplied electrically at one end. The latest generation of tubular fluorescent lamps in general has a tube diameter of approximately 16 mm or less, so that two or more lamps placed next to one another transversely to the tube length together occupy only little space. The holders for accommodating tubular fluorescent lamps are accordingly designed for contacting pin-shaped lamp contacts.
In a favorable embodiment of the luminaire according to the invention, in which the holders are suitable for accommodating tubular fluorescent lamps, the holders are present outside the reflector of the lamp housing. The holders do not emit light, neither do the portions of the tubular lamps adjoining thereto. If the holders and, preferably, also the dark bands of the tubular fluorescent lamps adjoining the holders on account of the positions of the holders are outside the reflector, said holders, and preferably said dark bands of the lamps, cannot absorb any light. This benefits the efficiency of the luminaire. It is favorable also for the heat balance, and thus for the luminous efficacy of the lamps, when end portions of the lamps lie outside the reflector owing to the fact that the holders are outside the reflector.
The lamp housing of the luminaire, and thus also the luminaire itself, is particularly compact if the surface area of the window accounts for 50 to 100% of the total surface area of the lamps to be accommodated in the holders enclosed by the reflector and the window. The luminaire then also has a good efficiency and a good light homogeneity.
The luminaire according to the invention is capable of generating white light with two lamps of different color temperature, which light may have all color temperatures lying between the color temperatures of said lamps in that one lamp is dimmed. Light can be generated with two lamps of different colors, which light has all mixed colors of said two colors, while it is possible to obtain all colors as well as white light having all color temperatures by means of three lamps having the primary colors red, green, and blue, respectively. A comparatively high light level can be obtained when the lamps are not or substantially not dimmed.
The lamp housing may have a variety of shapes. It may have, for example, a rectangular, for example square shape in cross-section, or alternatively round or oval. The lamps may be accommodated therein alongside the window, for example substantially parallel thereto. The lamps may then lie in a first plane, perpendicular to the window, or in a plane perpendicular to the first plane. Alternatively, the lamps may be placed on the edges of a virtual prism.
The reflector of the lamp housing may be diffusely or specularly reflecting. The reflector may consist of one or several separate bodies, or alternatively walls of the lamp a housing themselves may be the reflector. The reflector may be made of a painted material, for example metal, or of a synthetic resin, or alternatively it may have a metal reflecting surface, for example of aluminum, or a stack of layers of alternating refractive indices on a carrier, for example made of synthetic resin, thus forming a dichroic reflector. The reflection coefficient of aluminum used in luminaires generally lies between approximately 0.85 and 0.95. Dichroic reflectors in general have a reflection coefficient of approximately 0.93 to 0.995. If the window accounts for a comparatively small portion of the total surface area of the reflector and the window together, it is favorable to use a reflector having a comparatively high reflection coefficient.
It is possible that the reflector, for example a dichroic reflector, has at least a region which transmits a portion of the light which is not reflected. If the luminaire is mounted against or to a carrier, for example a ceiling, this embodiment of the luminaire may be useful for weakly illuminating the ceiling in the immediate surroundings of the luminaire.
The window may be white and light-scattering, for example have a light-scattering coating or may be made of a light-scattering material, for example polymethylmethacrylate (PMMA) with a coating thereon or a dispersion therein of, for example, a white fluorescent powder. Such powders have a low light absorption. It is advantageous if the window has approximately 50% transmission and approximately 50% reflection. Alternatively, the window may be made of transparent material and have a prismatic profile on its surface facing away from the lamps, so that it is light-transmitting and yet non-transparent. Such a window allows the generated light to pass in a narrower beam than does a light-scattering window.
The window may be regarded as a secondary light source. The emerging light may be directed and formed into a beam as though the window were a lamp. The means of the reflector housing may comprise reflectors laterally on either side of the window, concentrating the radiated light into a beam and at the same time screening off spatial angles laterally of the luminaire. It is achieved by means of this screening that, when the luminaire is fastened, for example against or in a ceiling, no light is radiated in lateral directions within the cut-off angle against the ceiling. The reflectors of the reflector housing may be accommodated in the reflector housing or may themselves form part of the housing. The reflectors may be made of usual materials such as, for example, synthetic resin, painted metal such as steel, aluminum, or of frosted, semi-bright, or mirroring metal.
The reflector housing may furthermore comprise means for concentrating light in directions transverse to the reflectors into a beam and cutting it off in those directions. These means may comprise, for example, lamellae which extend transversely between the reflectors opposite the window. The lamellae may be flat plates, or alternatively three-dimensional bodies, for example parabolically curved bodies.
The luminaire may be of multiple construction, for example with several windows in the same number of lamp housings together, for example, forming one constructional whole, and with several reflector housings. It is also possible for one lamp housing to have several windows. It then holds for the windows that their joint surface area lies between 10 and 70%, in particular between 50 and 60% of the total surface area of the windows and the reflector. A second window may then be arranged opposite a first window so that the luminaire is capable of giving light in two directions, for example direct and indirect lighting simultaneously.
Dimmers for controlling the power consumption of each of the lamps may be present in the luminaire or outside the luminaire, for example in a false ceiling.